1. Field of the Invention
The present invention relates a lens-fitted photo film unit with a flash device, and more particularly to a security device for the flash device, that makes the flash device unusable unless a restore signal is applied to the security device, thereby preventing unauthorized reuse of the flash device.
2. Background Arts
A variety of lens-fitted photo film units have been widely sold in the markets. The lens-fitted photo film unit, hereinafter called simply film unit, contains a roll of unexposed photo filmstrip and a cartridge shell, and has simple photographic mechanisms for exposing the filmstrip. Many kinds of film units are also provided with a built-in flash device. After being used up, the film units are recovered by their manufacturers for reusing some parts in new film units and recycling other parts as row materials.
However, there are some traders who collect used-up and emptied film units, and load unexposed photo film cartridges in the emptied film units for unauthorized sale. Since those traders do not make sufficient inspections on the recycled film units, nor repair inadequate part s of the film units, these unauthorized recycled film units may be of lesser quality than those recycled by authorized manufacturers. As the troubles with the recycled film units can smirch reputation of the film units in general, the film unit manufacturers have been trying to prevent the informal recycling of the film units by other traders.
In order to prevent that informal recycling, some film units are so designed that a functionally essential member has to be broken for disassembling the film unit. For instance, parts of unit housing are joined together by ultrasonic welding or the like, so these parts would be broken if they are forcibly separated. In other kinds of film units, a hook is formed with a part such that the hook pulls and breaks a functional member on another part when these parts are separated from each other.
As a preventive measure for that informal recycling, it is known in the art to electrically disable a photographic function of the film unit when all available frames have been photographed on the filmstrip or when the photo film cartridge is removed from the film unit. An exemplary of this type is disclosed in Japanese Laid-open Patent Application No.8-240884 (U.S. Pat. No. 5,517,265), wherein an IC with a counter is mounted in the film unit, for counting the number of frames. When the last available exposure is performed, an electric photographic device such as the flash device is disabled. In order to reuse the flash device, the manufacturer reads out an identification code from a memory of the IC through a specific external device, and inputs a reset code that corresponds to the identification code in the IC. Then the reset code is compared to an enablement code in the IC, and if the reset code and the enablement code are identical, the counter is initialized, and the photographic functions are recovered. Thus, the flash device comes to be reusable.
There are also those film units which contain a new type photo film cartridge called IX240 type. Because the photo film cartridge of this type uses a plastic shell, if ultrasonic welding is used for securing the parts of the unit body to each other, the plastic shell can be unexpectedly joined to the unit body. Therefore, it is hard to use ultrasonic welding for this type of film units. Concerning the second method of breaking a functional member by a hook, if the hook is not accurately formed, it can break the function part at the assembling, or cannot provide a sufficient effect. Beside these disadvantages, since a functional member of the film unit is broken, the manufacturer itself cannot reuse that member, so it is necessary to substitute a new one for that member in reassembling the film unit.
On the other hand, the method of electrically preventing the film unit from being informally reused is preferable in view of the fact that there is no need for breaking a functional of the film unit, and thus any functional member may be reused if its function has no problem. However, in order to make it hard for other traders to recover the function of the disabled film unit, the identification code or the enablement code must be a cipher code. In that case, it is necessary to provide a memory for storing the cipher codes, a data exchange circuit for exchanging the identification code and the reset code, a microprocessor and a memory for checking coincidence of the enablement code and the reset code. Therefore, a large scale circuit must be mounted in the film unit, so the cost of manufacture is increased.